This proposal seeks funding for an R21 grant under the NIH/NIBIB Exploratory/Developmental Research Grant Program to develop a novel integrated micro-transponder for wireless tumor tracking and in-situ radiation dosimetry. This microdevice will be an invaluable tool in radiation oncology for real-time received dosage measurements and tumor motion management. The primary envisioned application of the proposed device is for (1) Stereotactic Body Radiation Therapy (SBRT) treatments of thoracic and abdominal tumors and for (2) High Dose Radiation (HDR) treatment of prostate cancer. For SBRT applications transponders will be implanted in the tumor tissue and its vicinity for effective monitoring of dose delivery and tissue tracking at treatment. For HDR prostate cancer treatment the proficient application of the device would require its placement in the catheter passing through urethra to monitor dose along the radiosensitive membranous tube during implant or in the catheter attached to the balloon placed inside the rectum (balloon being utilized for better immobilization of the target and more favorable dose distribution in the rectum wall). For the radiation dose measurement, we will explore a device structure and detection scheme based on the depletion capacitance change associated with radiation-generated negative charge in the hafnium oxide gate of a metal-on-insulator (MOS) structure. In order to monitor tumor location in real-time, we will use a magnetic tracking method with superior signal- to-noise performance and enhanced interrogation range. Both of these devices will be integrated on the same silicon substrate and receive power from an inductively coupled link (no battery required), hence simplifying the packaging and encapsulation. Integrated Wireless Tracking and Dosimetry for Radiation Oncology This is a revised R21 application submitted in response to the NIH/NIBIB Exploratory/Developmental Research Grant Program to develop a novel integrated micro-transponder for wireless tumor tracking and in-situ radiation dosimetry. Although the reviews were positive (score 225), several concerns were raised by the panel which we have addressed in the present re-submission. The paragraphs that we have added or changed in response to the review use a different font (Palatino Linotype). [unreadable] [unreadable] [unreadable]